Interference suppression system for radio apparatus



Oct. 11, 1938. w. H. MYERS 2,132,875

INTERFERENCE SUPPRESSION SYSTEM FOR RADIO APPARATUS Filed Sept. 28, 1954 INVENTOR.

VI/ML/AM H MYAE'RS.

A TTORNE Y-S.

Patented Oct. 11, 1938 PATENT OFFICE INTERFERENCE SUPPRESSION SYSTEM FOR RADIO APPARATUS William H.'Myers, Detroit, Mich, assignor to The Crosley Radio Corporation, Cincinnati, Ohio, a

corporation of Ohio Application September 28, 1934, Serial No. 145,959

. 1 Claim.

In the operation of automobile radio sets, for example, considerable difficulty has always been had with extraneous noise in the receiver due to electrical disturbances set up by the engine and its associated electrical apparatus. Spark plug and generator suppressors have been used to good effect; but these add to the cost of the installation, and have not, inmany instances, entirely eliminated the noise It is an object of my invention to provide a new system for the suppression of electrical interference of this type, which is more nearly perfect in operation, which is adjustable to secure the effect desired, and which renders the use and expense of the ordinary suppressors unnecessary. This and other objects of my invention, which will be set forth hereinafter, or will be apparent to one skilled in the art upon reading these specifications, I accomplish by that process, and by that construction and arrangement of-parts of which I shall now describe an exemplary enibodiment,namely a system for automobile radio sets. It will be understood not only that modifications may be made in my invention without departing from the spirit thereof, but also that my invention can be applied to other sorts of mobile radio installations, such as those for airplanes, boats and the like, and even to stationary radio sets subject to electrical interference, where the conditions to be set forth hereinafter obtain, or can be made to obtain.

In the automobile, the antenna and its lead wire pick up not only the desired signal, but also static due to the electrical interference aforesaid. Briefly, in the practice of my invention I provide another collector which is adapted to pick up the electrical interference, but is shielded with respect to the desired signal. The interference voltage picked up by the second collector is attenuated and is fed to the receiving set in bucking relationship to the voltage picked up by the first collector. The noise voltages therefore cancel each other when the proper relationships obtain, leaving the clear signal voltage for amplification by the receiver. The conditions re ferred to, therefore, are such as permit the location of one collector to pick up signal and undesired radiations, and the location of another collector to pick up the undesired radiations while it is relatively shielded from the signal. It is not necessary that this shielding be perfect. The more perfect the shielding is, however, the less the desired signal will be cut in strength.

In the automobile, the hood, cowl and radiator form a shield about the engine, where the undethe art.

sired radiations originate. Since these parts are of metal, it is sufiicient to locate the second collector beneath the hood, where it .will be effectively shielded from thedesired signals. In other types of installation similar conditions prevail or can be caused to prevail, special shieldingof the second collector being employed if desired.

Reference isnow made to the drawing, wherein Figure 1 is a diagrammatic representation of an exemplary installation embodying my invention.

Fig. 2 shows a type of coil assembly useful for connecting the two collectors to the radio set.

Fig. 3 shows another form of coil construction for the same purpose.

Referring to Fig. l, I'have indicated diagrammatically the ordinary car antenna at I. I have indicated the engine at 2, and 3 represents the assembly of hood, cowl and radiator. 4 is a collector or antenna located within the shielded space 3, but adjacent the engine, This collector may be of any form desired. It may be a wire stretched beneath the hood; it may be a metal plate or a piece'of woven wire screen suitably supported on insulating members, or it may have any other form within the skill of the man in It will be seen that theantenna I is connected by means of a lead 5 to a primary coil 6, which may be shunted by a condenser 1. The collector 4 is connected by a lead 8 to another primary coil 9, which is likewise shunted by a condenser Hi. It will be seen that the primary coils B and 9, in their effect upon a secondary coil ll, located therebetween, are essentially out of phase. I prefer to make the condenser ID a variable condenser so that the phasing may be accurately controlled. The primaries 6 and 9 are connected together as at 12, and to a common ground l3. The coil II, which is a secondary coil, in its relationship to the primary coils 6 and 9,

- may be shunted as at [4 by the usual variable condenser for tuning purposes, and may be connected directly or indirectly to the first amplifying tube of the set in ways which will be Well understood.

For purposes hereinabove set forth, I prefer to attenuate the voltage picked up by the collector 4, and for this purpose I have shown a potentiometer 15 connected as at 8a to the primary coil 9, and as at IE to ground. The lead 8 from the collector 4 may be connected as at IT to the variable contact member of the potentiometer.

In the operation of my invention the antenna I serves as a first collector and picks up not only the desired signal, but also a certain amount of electrical interference. The antenna or second collector 4, being located close to the source of interference (in this instance the engine 2 and its associated electrical circuits) picks up this interference, but by reason of the fact that it is shielded by the hood and associated parts 3, the collector 4 picks up very little if any'signal. If now the voltage picked up by the collector 4 is attenuated to the proper value and is applied against voltage picked up by the antenna I so as to buck that voltage, it will be seen that the interference voltages may be caused to cancel each other. The signal voltage from the antenna I however, will not be so canceled. Ordinarily the collector 4 picks up substantially no signal voltage by reason of the shielding aforesaid. If it picks up a little signal voltage, this may cut down the signal voltage picked up by the antenna l, but the effect will be greatly minimized, especially by the attenuation of the voltage picked up by the collector 4 due to the action of the potentiometerl5.

The form factor of the coils 6, 9 and I4 is of importance in properly canceling the interference. A number of well known systems of winding may beemployed. I have shown in Fig. 2 a support [8 of insulating material holding a honeycomb coil 19, which is the secondary and which feeds the signal to the radio receiver, and a pair of .honeycombprima'ries 20 and 2! located upon opposite sides of the secondary l9. Adjustment may be had not only by varying the size and form of these coils, but also by varying the distance of primary coils 20 and 2| respectively from the secondary l9. 7

In Fig. 3 I have shown an insulating support 22, upon which is wound the secondary indicated at 23. The two primaries are wound together. as indicated at 24 and 25 about an insulating support 26, and there may be positioned betweenthe insulating support 26 and the secondary 23 an electro-static shield '21.

The main phasing is, of course, attained by the connections and associations of primary and secondary coils, but may be modified accurately as by means of the variable condenser It] in Figure 1. The modification of the interference voltage of the second collector to bring it to the value of the interference voltage collected by the first collector is likewise variable by means of a suitable attenuation deVice as vdescribed. These adjustments may be varied for different conditions.

When the proper adjustment has been reached, the operation of the radio set will be very quiet; and I have attained in this way under adverse circumstances, greater quietness of operation than I have found possible to attain by the other "means which have hitherto been suggested.

Modifications may be made in my invention without departing from the spirit thereof. The system as shown in my drawing is essentially -automobile,'and shielded from signal by said hood, 1

and means for applying the voltages picked up by said two antennas to said radio setin out of phase relationship, said means comprising a transformer having a coil connected to said radio set,'a second coil connected to said signal receiving 1;

antenna, a fixed condenser shunting said coil, a third coil connected to said second antenna, a

settable capacity shunting said third coil whereby phase adjustment may bemade in installing said radio set, said several coils being in inductive relationship, and the coupling between said coils being fixed, and a potentiometer with a leg to ground located in the connection between said third coil and said second antenna whereby to attenuatethe voltage picked up by said second antenna.

WILLIAM H. MYERS. 

